php單例模式(Singleton Pattern)執行個體教程

class DatabaseConnection { private static $db; private static $_handle = null; public static function get() { if ( self::$db == null ){ echo __LINE__; self::$db = new DatabaseConnection(); } return self::$_handle; } private function __construct() { $dsn = 'mysql://root:password@localhost/photos'; self::$_handle = 123; } } print( "Handle = ".DatabaseConnection::get()."\n" ); print( "Handle = ".DatabaseConnection::get()."\n" ); ?> 複製代碼 9Handle = 123 Handle = 123 [Finished in 0.1s] 例2，php單例模式。 class DatabaseConnection { public static function get() { static $db = null;//此處將樣本1的靜態成員變為靜態變數 if ( $db == null ){ echo __LINE__; $db = new DatabaseConnection(); } return $db; } private $_handle = null;//此處將表示樣本1的靜態去除 private function __construct() { $dsn = 'mysql://root:password@localhost/photos'; $this->_handle =123; } //此處新增擷取私人成員$_handle的方法 public function handle() { return $this->_handle; } } print( "Handle = ".DatabaseConnection::get()->handle()."\n" ); print( "Handle = ".DatabaseConnection::get()->handle()."\n" ); ?> 複製代碼 8Handle = 123 Handle = 123 [Finished in 0.1s] 這兩個樣本個人偏好第二個 四。限度可產生執行個體的個數 class DatabaseConnection { public static function get($persistent_id=0) {//傳入一個標識 static $db = array();//此處改為數組 if ( !array_key_exists($persistent_id, $db) ) { echo __LINE__; $db[$persistent_id] = new DatabaseConnection(); } return $db[$persistent_id]; } private $_handle = null; private function __construct() { $dsn = 'mysql://root:password@localhost/photos'; $this->_handle =123; } //此處新增擷取私人成員$_handle的方法 public function handle() { return $this->_handle; } } print( "Handle = ".DatabaseConnection::get(1)->handle()."\n" ); print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" ); print( "Handle = ".DatabaseConnection::get(2)->handle()."\n" ); ?> 複製代碼 6Handle = 123 6Handle = 123 Handle = 123 [Finished in 0.1s] 補充，利用static靜態化的方法使我們可以輕鬆地實現php的單例模式。當然也可以使用全域變數儲存，但是這種方法僅適用於較小的應用程式。在較大的應用程式中，應避免使用全域變數，並使用對象和方法訪問資源。

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